Terminals, such as smartphones or personal computers (PCs) are nowadays capable of activating and using a plurality of logic interfaces associated with one or more physical interfaces. Such terminals are said to be multi-interface (MIF) terminals.
A plurality of IP addresses can be allocated to such MIF terminals so that they can connect to different types of network such as a fixed network, a mobile network, or a wireless local area network (WLAN), where the emblematic example would be a WiFi network, and in a manner that may be simultaneous or deferred. These IP addresses may:                belong to the same family of addresses or to different families of addresses (IPv4, IPv6, or both);        have different lifetimes;        have different scopes, e.g. a private IPv4 address, a unique IPv6 address of local scope (i.e. a unique local address (ULA)), or an IPv6 address of global scope (global unicast address (GUA)); and        be allocated to the same logical network interface or to different logical network interfaces.        
Nevertheless, it should be observed that the “MIF” characteristic is volatile, since the ability to use a plurality of interfaces depends on conditions of connection to the network(s), on the location of the device, or on other factors. An MIF device may in particular make use of a plurality of interfaces that are available to it while setting up a simple connection (i.e. a connection set up along a single path with a given third party), or after setting up a simple connection. It may also be observed that a device does not know a priori whether it has the possibility of using a plurality of distinct paths for setting up a communication with a given third party. More precisely, the device acquires this information (where appropriate) only at the end of a stage during which it attempts to set up a multipath connection with the third party.
When a terminal has a plurality of interfaces capable of connecting to different types of access network (e.g.: fixed, mobile, or WLAN), it then benefits from access that it said to be “hybrid”, since it combines different access network technologies. The services on offer concerning a terminal having hybrid access rely on introducing functions in the network that make it possible to aggregate all of the network connections of a terminal (e.g.: WLAN and 3G, or ADSL, WLAN and 4G).
In this respect (cf. Wikipedia) it should be recalled that in the field of networks, the term “aggregating links” designates grouping together a plurality of network interfaces as though they constituted a single interface, in particular for the purpose of increasing throughput beyond the limits of a single link, and optionally for ensuring that other interfaces take over in the event of a network link failing (redundancy principle). Link aggregation applies to any type of traffic conveyed along such links, including IP traffic.
Link aggregation may also be used to share traffic over a plurality of links. Under such circumstances, the way traffic is shared among the links/interfaces making up an aggregate of links depends on various parameters; for example, it depends on the type of traffic (such as TCP or UDP), or on the traffic engineering policy (such as the required quality of service (QoS)).
It should be observed that link aggregation makes no assumption concerning the configuration of the remote machine. Thus, a source machine may activate a link aggregation procedure without the remote machine using such a function.
Various modes of aggregation may be envisaged, including the following three modes:                backup mode: this mode consists in using secondary paths in the event of primary paths being unavailable, with this being for the purpose of improving the availability of the network and thus the robustness and the reliability of IP connections set up over the various links;        bonding mode: this mode consists in using the resources associated with some or all of the available paths, the IP streams associated with a given application possibly being shared among a plurality of paths; the decision to use all of the paths, or only some of them, may for example be conditioned by the nature of the traffic or the availability or reliability characteristics associated with each path, which characteristics may vary greatly from one path to another; all of the paths selected for this bonding mode are considered as being primary paths; and        a “comfort” mode: this mode is similar to the bonding mode, except that the streams of a given application are not shared among a plurality of paths, but are sent over a single path.        
It should be observed that these modes are not mutually exclusive, and that they are not specific to any one particular type of traffic. Thus, they may be put into place independently of the nature of the traffic that is to be conveyed along paths aggregated in one or another of the various modes.
The term “network connection concentrator” is used to designate any network function making it possible to aggregate the connections making use of the various paths that can be used by a device in order to set up communication with a remote device. The use of a network connection concentrator has in particular the effect whereby a connection that is seen by a local device as being a multipath connection may be seen by a remote device as being a simple connection.
By way of example, a network connection concentrator may be a function incorporated in a residential or business gateway, or it may cohabit with a multipath TCP (MPTCP) or a stream control transmission protocol (SCTP) proxy function or with a generic routing encapsulation (GRE) tunnel termination point, or indeed with a termination point of IP-in-IP tunnels or of level 2 tunnels. Where appropriate, the aggregation of all of the multiple paths by a network concentrator may lead to one or more virtual tunnels being set up, e.g. in order to facilitate management operations associated with setting up the communication (by isolating the traffic characteristic of the communication set up over the various paths as aggregated in this way, and improving the process for detecting failures).
FIGS. 1a, 1b, and 1c show various types of architecture associated with network connection concentrators.
These figures show a terminal T connected to one or more IP networks. The natures of these various access networks may be wired, wireless, or other; furthermore, these accesses may be multiple, i.e. the terminal T may have the ability to connect to different access networks simultaneously, or otherwise.
The terminal T is connected to the IP networks via N nodes (P1, P2, . . . , PN) having a network connection concentrator function. By way of example, such a node may be a gateway (residential or business) or an IP router. In the figures, it can be seen that:                the terminal may be connected to a single network managed by a single IP connectivity provider who has deployed at least one network connection concentrator (FIG. 1a); or        the terminal may be connected to m networks R1, . . . , Rm all of which host at least one network connection concentrator (FIG. 1b); or indeed        the terminal may be connected to m networks R1, . . . , Rm, some of which host a plurality of network connection concentrators (FIG. 1c).        
Nevertheless, using multiple paths for setting up communications raises problems of various kinds.
It is commonly accepted that the use of load sharing mechanisms between a plurality of paths needs to ensure that those paths possess a comparable level of quality of transfer, in particular so as to avoid weakening the integrity of the data that is characteristic of a given connection and that is exchanged over those various paths (the quality of transfer may be characterized by a plurality of parameters including, in particular: latency, jitter, and rate of packet loss).
When a terminal benefits from hybrid access, its actual ability to make use of all of its interfaces is generally associated with the quality of each of the access networks in question, as perceived by the terminal. This quality may be expressed in terms of available bandwidth, of time to access the desired content, or indeed in terms of variation in the delay for transmitting two consecutive packets. This quality naturally varies from one access network to another, and may present differences that can be so great as to compromise setting up a multipath communication over the various access networks; the risk of a loss of integrity of the streams exchanged during the communication increases with any increase in such differences, to such an extent that the communication might become unintelligible. The aggregated link will present quality that depends in particular on the location of the network connection concentrator.
These different quality levels can compromise setting up additional subflows in the context of a multipath connection. The above-mentioned magnitude of the risk of integrity loss might incite the terminal to set up a simple connection only, even though that means losing the benefits characteristic of a multipath connection, such as optimizing available resources in terms of bandwidth.
Such a risk is also made worse in the context of a terminal that does not have its own means enabling it to set up a multipath connection, and doing this by calling on a network connection concentrator deployed in the access network to which the terminal is connected. In this context, the question of different levels of quality associated with using the plurality of available concentrators (e.g. depending on the location of the remote terminal with which the terminal seeks to set up a communication) becomes correspondingly more complex to solve when the terminal does not necessarily have the information and the intelligence required for selecting the concentrator that presents the best guarantees of quality, e.g. depending on the nature of the traffic, of the application, or of the service associated with the communication.